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The Olfactory Organ

As is well known, the gnathostomatous vertebrata may be divided into monorhinous and amphirkinous forms. By their monorhinous condition the Cyclostomes stand in contrast to the rest of the vertebrates. KupfTer (1884) has sought to bridge the gap between the two conditions, and his views have for that reason secured much acceptance. He regards the ciliated groove at the anterior neuropore of Amphioxus as an olfactory organ. The Cyclostomes, in addition to the unpaired anlage of the olfactory organ, the " unpaired olfactory placode," situated close to the neuropore, had also paired organs situated more laterally, the lateral " olfactory placodes," which secondarily fused with the unpaired one ; the rest of the vertebrates in addition to the lateral olfactory placodes had also the anlage of the unpaired placode, but this latter degenerated.

This view has been opposed by Peter (1901) ; he contends that an unpaired olfactory plate occurs in the rest of the vertebrates in the region of the neuropore, and I can from my own observations confirm his statements. The first anlage of the olfactory organ in man is formed by a paired convex area, covered by thickened epithelium (sensory epithelium), situated near the point where the anterior neuropore has closed. A%n Wyhe (1882) has maintained that the olfactory nerve is only apparently the first cranial nerve ; in reality it is the second, the optic being the actual first and the succession being reversed by the cranial flexure. This would also be the case with the corresponding sense organs. Nussbaum (1900) has also reached the same conclusion, and says, "Consequently the spot where the optic anlage leaves the brain has been secondarily transferred from the dorsal to the ventral surface and at the same time pushed caudally, on account of the forebrain flexure. By this the optic nerve, as Van Wyhe has already pointed out, has become the second cranial nerve, although it was originally on the dorsal surface in front of the olfactory nerve, which is counted as the first cranial nerve in adult vertebrates." Hatschek (1909) has also quite recently made the same statement. The question depends upon what is to be regarded as the anterior end of the medullary plate. If the infundibulum represents its original anterior end and the regions of the chiasma and the recessus opticus have been formed by suture, and if the optic vesicles, as must also be assumed, are dorsal structures corresponding to the part of the edge of the medullary tube which has in this region united by suture, then Van Wyhe is correct. I re gard this primary question, however, as not yet settled, and accordingly cannot regard it as settled that the olfactory nerve really lies caudal to the optic (compare also Keibel; 1889).

The sensory epithelium of the olfactory placodes is at first, especially ventrally, imperfectly marked off from the epithelium that covers the rest of the head. This condition was found by Keibel and Elze (Fig. 127) in an embryo of 4 mm. in its greatest length (Normentafel, Plate 10) ; the olfactory areas were already distinguishable in an embryo of 3 mm. described by Bromann (189G) (Normentafel, Plate 11), while Hammar (Normentafel, Plate 9) could not find them in an embryo with a greatest length of 4.7 mm.

The delimitation of the olfactory epithelium is more perfect in the embryo of Plate 14 of the Normentafel (4.9 mm. nape-breech length, 4.7 mm. vertex-breech length) (Fig. 128). x In an embryo with a greatest length of 5.3 mm. (4.6 nape length) the olfactory areas are still convex, but are beginning to be more sharply delimited dorsally. They then become flattened (Fig. 129) (Normentafel 21, greatest length 6.75 mm.) and later begin to be depressed in their dor so-lateral part (Fig. 130) (Normentafel, Plate 24, in an embryo of 6.5 mm. greatest length = nape-breech length, vertex-nape length 4.7 mm., vertex-brow length 3.0 mm., age fairly certainly 21 days ; also Normentafel, Plate 25, greatest length = nape length 6.25 mm.). In an embryo of 8 mm. (Normentafel, Plate 30 and Fig. 21 b) the olfactory area, according to Hammar, is feebly depressed, and in its caudal portion, which has deepened into a pocket, the nasal groove has formed. This embryo corresponds with that which His (1880-1885) figured in Fig. 29, p. 46, of the third part of his Anatomie menschlicher Embryonen, and which has also been figured by Kallius (1905) and has formed the basis of his description; I repeat His's figure here as Fig. 132 for comparison, although I have some doubts whether it correctly represents the normal conditions. The nasal fossa is surrounded by a marginal swelling which is interrupted below toward the maxillary process. The lateral limit of the swelling covers only a part of the medial wall of the nasal fossa. A process on the medial limb His identified as the processus globularis (p. g.?), and further down, where the medial edge comes into relation with the maxillary process, there is a larger projection, and internal to this a small round, rather deep and sharply margined depression (J. 0.?), which His regarded as the earliest anlage of Jacobson's organ. I have never seen the earliest anlage of Jacobson's organ of this form in man, it appears in my opinion as a groove, and the projection also which His identifies as the processus globularis I would not so identify, but would suggest that the swelling near the maxillary process and external to the depression designated by His as Jacobson's organ is much more probably the structure that should be identified with the processus globularis. I follow, accordingly, my own observations here and must leave it for later investigations to decide which are correct.

1 Delia Vedova (1907) has already described olfactory fossae in an embryo of 4.7 mm.

Some further observations are necessary for a comprehensive account of the development of the nasal fossae, and the formation of the face must be recalled. In a stage such as that shown in Fig. 133 the oral fossa is bounded above by the frontal process, to the right and left by the maxillary processes, and below by the mandibular processes. Since a. projecting angle is formed where the right and left mandibular processes meet % the entrance into the oral fossa has a pentagonal form. The two upper lateral angles, where the maxillary processes are better developed, extend as the lachrymal grooves as far as the eyes; they therefore bound the frontal process laterally. In the territory of the frontal process there is now formed, as we have seen, on either side a nasal area (His). 2 The nasal area is at firsl convex, in correspondence with the form of the surface of the frontal process, and even when the epithelium has become sharply delimited on all sides it is not recognizable on superficial examination. Only when it becomes flattened, and especially when it begins to be depressed, is it distinct. These first processes may be determined essentially by growth of the epithelium covering the nasal area (Peter, 1900 and 1902), but in man observations for determining this point have not been made. Later the margins of the area become raised by the growth of the surrounding mesoderm and thus deepen the nasal fossa, or rather the nasal grooves, for the wall surrounding the olfactory area is interrupted orally. In this stage, shown in its earliest stages in Fig. 134, the anlagen of the olfactory organ are separated by almost the entire breadth of the frontal process. It is customary to term the portion of the frontal process lying between the areas the middle frontal process and the lateral portions the lateral frontal processes; these latter coincide almost exactly with the lateral nasal processes, which project lateral to the olfactory grooves. Quite different is the relation of the medial nasal processes to the middle frontal process; they originally occupy only a very small lateral portion of it. The further transformation of the nasal grooves into the primitive nasal cavities is brought about by the maxillary processes coming into contact and fusing with the lower ends of the medial nasal processes. These lower ends project markedly forward and are known as the processus globulares (His). The fusion takes place from within outwards and occurs as the processes meet, so that the primitive nasal cavities in man, as in the rest of the mammalia, 3 are never connected by a groove with the primitive mouth cavity ; there is no reservation of a choana, so that the primitive nasal cavities, which open anteriorly by the external nares, are blind

Fig. 132. — (After His, from Anat. Menschlicher Embryonen, III, p. 46.) X 20. View of the anterior portion of the head of a human embryo from the left side. P. g f, marked by His (without ?) as the processus globularis; J . O t, marked by His (without f) as Jacobson's organ.

Fig. 133. — Head end of an embryo seen from in front. (After Rabl, Entwicklungsgeschichte des en face. (After Rabl (1902), Entwicklungsgeschichte Gesichtes, 1902, and corresponding practically with des Gesichtes.) This corresponds almost with Fig.

sacks and are at first shut off from the mouth cavity (Hochstetter, 1891 and 1892, Keibel, 1893, Delia Vedova, 1907). By the coming in contact of the maxillary processes with the processus globulares, the nasal grooves become gradually closed and the external nares more and more narrow; finally, the lateral nasal process comes into contact with the medial one and assists in bounding the primitive nasal cavity laterally and below, as I can state in confirmation of Peter's (1902) results. At the close of this developmental process (Fig. 135) the upper border of the mouth is formed by the maxillary processes and the medial nasal process and the lower border of the nares by the medial and lateral nasal processes. (Compare also Vol. I, p. 83, Fig. 64.) The primitive nasal cavities are shut off from the palate, but their epithelium is in connection with that of the mouth cavity by a plate of epithelium (Fig. 136). While this epithelial plate becomes transformed at its posterior end into a membrane, the bucconasal mem

brane (Hochstetter), and finally tears, the primitive choanae being thus produced, the mesoderm of the maxillary processes and of the lateral nasal processes is growing toward that of the medial nasal processes; it eventually destroys the epithelial plate and forms the primitive palate. This can be regarded as consisting of a facial portion, from which the upper lip is formed, and an oral portion, the premaxillary palate. The mesoderm of both portions is furnished by the maxillary and medial nasal processes, the lateral nasal processes participating only at the lower border of the nares.

While the developmental processes just described have been taking place, the middle frontal process has been gradually becoming smaller and the two nasal openings have been brought closer together. On the middle frontal process there may be distinguished laterally the medial nasal processes, each ending in a processus globuiaris, between these the trough-like depressed infranasal area (His), and above this the area triangularis (His), above which, again, is the part of the head which projects owing to the anlagen of the cerebral hemispheres (Fig. 135). The infranasal area is separated from the area triangularis by an angle that is at first indistinct but later becomes more sharply defined and from which the border and tip of the nose are formed; the area triangularis becomes the dorsum of the nose and the infranasal area is transformed into the septum. His believed that the nasal septum had a paired origin, because in the stages in which the nasal openings are close together the medial nasal processes are almost in contact in the median line and the whole of the portion of the middle frontal process lying between them has become a

rather deep groove. This groove may, as a rule in many animals but exceptionally in man, persist, forming a median lip cleft. Normally this embryonic cleft closes by the growth of the mesoderm forcing the epithelium out of the cleft, not by the medial nasal processes coming into contact and uniting, so to speak, by a suture. In my opinion, therefore, it is not proper to speak of an actual paired anlage of the nasal septum, although the material for it is thrust in toward the median line from the right and the left.

We have now in the first place to consider the anlage of the organ of Jacobson and that of the conchce, and then the transformation of the primitive into the definitive nasal cavities.

The organ of Jacobson 4 in man appears as a groove-like depression on the medial wall of the olfactory fossa. I have seen its earliest anlage in an embryo of 8.5 mm. greatest length (Normentafel, 32). Fig. 137 shows it in section in an embryo of 9.2 mm. greatest length, 8.8 mm. NL. (Normentafel, Plate 38). It is seen further developed (Fig. 136) in an embryo of 14 mm. (Normentafel, Plate 51). The groove has deepened and it then closes from behind forwards. The mouth of the cylinder produced in this way narrows, and on its medial wall there forms olfactory epithelium, in connection with which, however, no cilia have yet been observed ; glands also develop. In the human fetus the organ lies in the anterior portion of the nasal septum ; in a fetus of about ten weeks Kallius (1905) found it on both sides with a length of 0.42 mm.; its entrance was narrow and led into a greatly (about tenfold) enlarged sack. About this time one can readily observe, as Kolliker first pointed out, that branches of the olfactory nerve pass from Jacobson's organ to the brain. 3 In the twentieth week of fetal life the organ, according to Kallius, has reached the height of its development. Later it varies greatly and may completely degenerate, even in the embryo, but, on the other hand, it is not infrequently found and has often been described in the adult. (Compare on this point Merkel, 1892.)

Fig. 138. — Section through the head of a human embryo of 18.5 mm. greatest length. (Collection of Robert Meyer, No. 32; Normentafel of Keibel and Elze, Plate 64, Fig. XXI.) X 15. G.L., palatal process; J.O., Jacobson's organ; point of union with the nasal cavity; S., nasal septum, in which there is a common blastema for the cartilage of the septum and Jacobson's cartilage; Z., tongue, in which the musculature is beginning to differentiate. The tongue (Z) lies between the palatal processes. An early stage of the dental ridges may be recognized.

Fig. 139. — Section through the head of the embryo of Fig. 13 !. The section lies 150 m further caudad. The cerebral hemispheres and one eye have been cut, but Jacobson's organ is no longer visible. The lingual and hypoglossal nerves are entering the tongue. The lettering as in Fig. 138. X15.

A case in which it was present in the adult in a quite exceptional degree of development has recently been recorded by Mangakis (1902). Although Peter (1901 2 , p. 71) again repeats the view already frequently stated, that the organ is often destroyed in extra-uterine life as the result of frequently occurring catarrh of the nasal mucous membrane, yet I agree with Merkel (1892) that there are no sufficient grounds for this opinion, since the organ often disappears in the fetus. A supportive apparatus for Jacobson's organ is also formed, Jacobson's cartilages. According to Mihalcowics (1898), these cartilages separate from the cartilage of the nasal septum, but, like Kallius (1905), I find that they arise independently. At first only one cartilage anlage is to be seen on either side, "but in the fourth to the fifth month one sees several, usually three, a larger one that is frequently somewhat curved, and two smaller" (Kallius). Originally also the cartilages are situated close to the organ of Jacobson, but later they separate from it. Their relationship to Jacobson 's organ has been called in question and they have been described as the vomero-nasal cartilages (see Spurgat, 1893 and 1896) ; in my opinion this is incorrect, for comparative embryology shows that these human cartilages are to be homologized with the typical Jacobson 's cartilages of the mammals. How the comparison is to be followed out in detail, when in later stages three cartilages are present, will be considered further on. Delia Vedova (1907) believes that the lateral wall of the cartilaginous nasal skeleton also takes part in the formation of these cartilages, and, with Mihalcowics (1898), regards them as the remains of a plate that in other animals closes the nasal cavities below. That Gegenbaur (1886) should deny the occurrence of an organ of Jacobson in man, when the relation of the olfactory nerve to the organ during development had previously been clearly shown by Kolliker (1883), is surprising.

Gegenbaur identifies the structure that is here described as the organ of Jacobson with the septal gland first described by Steno. From what has been said, there cannot be any doubt but that in the human Jacobson's organ we have a portion of the olfactory organ which possesses special functions in many animals, but has become rudimentarv in man.

Some stages in the development of Jacobson's organ are shown in Figs. 139 to 144, and the development of Jacobson's cartilages may be followed in Figs. 138, 139, 140, 143, and 144. It will be seen that they arise from a blastema common to them and the cartilage of the nasal septnm (Figs. 138 and 139) ; from their first appearance, however, they are sharply marked off from the cartilage of the septum (Fig. 140). Fig. 141 shows the right side of the nasal cavity under higher magnification. The formation of nerves in connection with the organ of Jacobson is taking place, and in the epithelium of the nasal cavity a peculiar doublelayered condition is noticeable. The most superficial cells are arranged like a covering layer, except in those regions which are already recognizable as sensory epithelium. The same condition obtains also in older stages, as may be seen from Fig. 143 (fetus of 4.2 cm. sitting height), and it certainly deserves a thorough investigation. Fig. 142 shows a stage intermediate between Figs. 140 and 143. The palatal processes have come into contact, but the epithelium has not yet been forced out by connective tissue along the line of suture. The right and left nasal cavities are still in continuity below the septum. Fig. 144 shows some sections taken from a frontal series through a fetus of 47 mm., the sections following one another in apicocaudal direction. In Fig. 144, A, two very short lateral processes {p) branch out from the septal cartilage and very soon separate from it (Fig. 144, B, p), but the septal cartilage, which is very thin in places, is never connected with any of the other cartilages. Basal from these processus laterales ventrales (Zuckerkandl, 1909) there then appears on either side a cartilage plate (Fig. 144, C, pi), which soon divides into a medial and a lateral portion (Fig. 144, B, I and m) . While first the cartilage indicated by I and then that indicated by p disappear, a small piece separates from m (Fig. 144, E and F). According to Zuckerkandl (1909), this much is at least certain, that the medial portion of the plate pi becomes Jacobson's cartilage and that the portion p is to be homologized with the processus nasalis lateralis of other forms. He does not suggest an homology for the cartilage I.

Fig. 141. — A portion of the right side of Fig. 140 more enlarged. X 95. J.O., Jacobson's organ; U.M., inferior concha (maxilloturbinal). Over a considerable portion of the epithelium of the nasal cavity there is a sort of covering layer.

The development of the concha takes place entirely in the region of the sensory epithelium, — that is to say, in the region of the primitive nasal cavities. The conchal apparatus of the human nose, like the human olfactory organ in general, is reduced, so that it is impossible to obtain a satisfactory understanding of it without the aid of comparative anatomy and embryology.

The way toward a satisfactory understanding of it has been shown especially by the work of Killian (1895, 1896, 1902) and Peter (1902 2 ); but the observations of Zuckerkandl (1887, 1892 x and 1892 3 ) and Schonemann (1901) should also be mentioned. According to Peter, the conchae arise as well on the lateral as on the medial wall of the primary nasal cavities, 6 the maxilloturbinal and nasoturbinal arising from the lateral and the ethmoturbinals from the median wall. Fig. 145 shows a section through the posterior portion of the olfactory fossa of a rabbit embryo of 3.5 mm. head length; the dorsal region of the medial wall is slightly bent away from the lateral one, and the slight swelling above the bend represents the first ethmoturbinal. How it is transferred from the medial to the lateral wall is made clear by Fig. 146 ; it is brought about by the ingrowth of the epithelium at x. In a similar manner two other ethmoturbinals are formed independently from the septal wall in the rabbit, in the region of the posterior blind sack of the nose (Fig. 147). The one which is first formed is in embryonic life completely divided into two secondary ridges by a groove. From the lateral wall the conchal structures which Peter terms the conchas obtectse are formed below the rostrally projecting border of the first ethmoturbinal. In front of these, in the region of a cleft which is bounded anteriorly by the sharply marked posterior border of the nasoturbinal (the processus uncinatus), the maxillary sinus is sinking in in a downward direction.

Peter has made it probable that the ethmoturbinals are formed from the medial wall in man also, but he has not been able to demonstrate it. As a difference in the human development as compared with that of the rabbit, it may be noted that the nasoturbinal is very rudimentary and develops very late; it becomes the agger nasi (Peter, 1901 2 , p. 64). In early stages the maxilloturbinal alone is present; it occupies the posterior two-thirds of the lateral wall throughout its entire height. Gradually it becomes more sharply marked off, especially ventrally; the groove thus formed becomes the inferior nasal meatus. It is interesting to note that in man a dorsal lamella is added to this concha in the fourth month (Mihalcowics, 1896 2 , p. 71), 7 so that at this stage it recalls the doubly coiled maxilloturbinal of many mammals. Only late does the agger nasi appear as a slight elevation above the inferior concha and in front of the first ethmoturbinal. In an embryo of 30 mm. vertex-breech length Peter finds a second ethmoturbinal behind the first, and behind this still other four in maximo may appear (Killian). That a new ethmoturbinal is interposed and grows out between two of those already present, as Zuckerkandl supposes, I cannot admit; nor can I agree with Delia Vedova's (1907) criticisms of Killian, whose preparations I have seen.

Fig. 144. — Frontal sections through the nasal septum of an embryo of 47 mm. The sections have been taken from a series passing in the apicocaudal direction. (After Zuckerkandl, 1909.) 8, septum: p, ventral lateral process: pi, cartilage plate below p: m and I, portions formed from cartilage pi; according to Zuckerkandl, m becomes Jacobson's cartilage.

In the description of the succeeding developmental processes I follow Killian, differing from him only in that, with Peter, I do not term nasoturbinal (agger nasi) ethmoidale I, but contrast the nasoturbinal, maxilloturbinal, and conchae obtectae as lateral conchae with the ethmoturbinals which are medial conchae. Killian 's ethmoturbinale II is accordingly termed ethmoturbinale I in the figures taken from his works, and similarly with the others. Killian has acquiesced in this alteration of his nomenclature.

Figs. 148 and 149 show the lateral nasal walls of two fetuses of the ninth to the tenth months; Fig. 150 is a combined diagrammatic figure representing the maximal number of ethmoidalia, an arrangement that only very rarely occurs. In addition to the maxilloturbinal and the nasoturbinal (agger nasi) five ethmoturbinals may be recognized, the free edge of each of the anterior ones forming a cms ascendens and a cms descendens, while where the two crura meet there is a more or less pronounced lobulus with a nodulus, which is to be compared with the tip of the ethmoturbinals of the mammals. In addition to these principal conchae Killian finds other accessory conchae in the principal grooves, and accessory grooves may also develop on the conchee. Fig. 151 shows the middle meatus of a human embryo of the sixth month ; the anterior part of the middle concha has been removed. One sees between the bulla ethmoidalis, which is formed by two conchas obtectae, and the processus uncinatus the inf undibulum ; in it lie three infundibular accessory conchae ; the groove between the upper and the middle one is marked Sim^s. Above the bulla ethmoidalis and the inf undibulum lies the upper part of the recessus ascendens, the frontal recess, with three frontal conchae bounded by four grooves. The development of the nasal cavities is complicated by the formation of the sinuses and the ethmoidal cells ; also fusions of grooves and parts of grooves occur (Killian), a phenomenon that may, at least in part, be regarded as a compensation for growth processes (Schonemann, Peter). Killian 's account is followed here. The three posterior crura ascendentia fuse throughout their whole extent, but only the anterior borders of the anterior three fuse, in such a manner that each unites with the upper surface of the next succeeding concha; thus recesses are formed under the anterior parts of the conchae, the recessus ascendentes, the first of which is the recessus frontalis, already mentioned. The rami descendentes IV-VI become completely obliterated, but the anterior three only partially, so that the free margins persist and form the definitive conchae, which, accordingly, represent only the crura descendentia of the original principal conchae. From recessus ascendens III a posterior ethmoidal cell may be formed frequently a cell then unites with it, which has its origin from the portion of the groove corresponding to the ramus descendens. The superior recess of the second groove also becomes a posterior ethmoidal cell, the groove itself becomes two cells, an upper and a lower, which are separated by an accessory concha (Killian, 1895 2 ). From the recessus superior of the first groove, whose upper part Killian has named the recessus frontalis, the upper and anterior ethmoidal cells (frontal cells) arise.

Fig. 151. — Middle nasal meatus of a human fetus of the sixth month. The anterior part of the middle concha, ET.I, has been removed. There are to be seen above the bulla ethmoidalis (Cim\ s.) and the processus uncinatus (Pr. u.) three frontal conchae (C. /1-3) on the lateral wall of the frontal recess and bounded by four frontal grooves (S.fi-t). (After Killian, Arch, fur Laryngologie, vo' 13.) MT., inferior concha (maxilloturbinale) ; Simi S., groove between the upper and middle infundibular accessory conchas.

In addition the recessus frontalis gives origin to the sinus frontalis ; indeed it may be completely transformed into that cavity or else the sinus is formed by one of the frontal cells protruding between the frontal conchas mentioned above. These concha? themselves usually vanish completely by fusing with one another and with neighboring structures; the third one may fuse with the upper end of the bulla ethmoidalis. The frontal sinus grows very slowly; it is still wanting at the time of birth (Delia Vedova, 1907) and at puberty has only the size of a pea.

The maxillary sinus develops at about the middle of the third month of intra-uterine life from the recessus inferior of the first groove. 8 At first it is only a small depression, which soon becomes a sack. In correspondence with its point of origin the fully formed sinns opens usually into the most posterior and lower portion of the infundibulum. Only after the eruption of the milk-teeth does it enlarge and begin to assume its characteristic pyramidal form; up to the fifth or sixth year of life it is round. In 10 per cent, of cases there now arises above the centre of the middle concha an accessory opening. The sphenoidal sinus is the most posterior part of the nasal cavity itself, separated by fusion processes ; as it increases in size it gradually penetrates the body of the sphenoidal bone. Two diagrammatic horizontal sections (Fig. 152, a and b) through the right half of the nose show clearly the relation of the embryonic arrangement to that of the adult.

According to Vedova (1907), it forms in the first half of the third month.

The inferior concha is the maxilloturbinal of comparative anatomy and the agger nasi the nasoturbinal. The middle concha is derived from the descending and a small part of the ascending portion of ethmoturbinale I.

The superior concha, when it is present, corresponds to the descending portions of ethmoturbinalia III and IV.

The superior meatus corresponds to the descending ramus of the second groove, the supreme meatus to the descending ramus of the third groove.

The accessory spaces may be classified as in the following table, in which the spaces between two principal conchae are regarded as of the first order, those between principal and accessory conchas as of the second order, and those between two accessory conchas as of the third order.

The septal folds, plicae septi, which may be seen on the nasal septum in fetal life, have nothing to do with the formation of the conchae; they lie in the region of the vomer and were seen and figured by Euysch (1703). Killian (1895) has studied them carefully and Figs. 153, a and b, are taken from his paper. Even in a three months ' fetus the epithelium in this region is thicker than elsewhere on the septum and the septal folds are formed by the ingrowth of furrows covered with epithelium. 9 They can first be recognized with the naked eye in the fourth month ; from that time on the proportion of septa on which they may be seen increases until the end of the eighth month and then diminishes again until birth. After birth the folds usually disappear ; if they persist they not infrequently form, by hypertrophy, tumor-like structures in the adult.

The development of the olfactory nerves has not been carefully investigated in man, but there is no reason for supposing that it takes place differently from what occurs in other vertebrates. In these the olfactory fibres are formed as outgrowths from the basal portions of the olfactory cells, extending to the brain. Some cells also wander out from the epithelium and are later to be found scattered along the entire length of the olfactory nerves, appearing like ganglion-cells ; their processes extend on the one hand to the olfactory epithelium and on the other to the brain. It has already been stated that olfactory nerve-fibres also develop from Jacobson's organ. Why nerve-fibres develop from only a very small portion of the primitive sensory epithelium of the olfactory fossa becomes clear when it is remembered how small the olfactory region of the fully developed nose is in comparison to the relative area of the primitive nasal fossa. For data on this point reference may be made to the observations of Brunn (1892), to Kallius in von Bardeleben's Handbuch, and to the account, given later on, of the relation of the primitive to the definitive nose.

Fig. 153b. — The same septum as is shown in Fig. 153a. The boundary of the vomer is shown (V.), otherwise the lettering is as in Fig. 153a.

The glands of the human nose, the small Bowman's glands, develop in the third and fourth months as solid processes. "In the new-born child they are weakly developed on the floor of the nasal cavity, but more abundantly on the medial surface of the inferior concha" (Kallius, 1905). They reach their complete development only after birth. 10 Delia Vedova (1907) states that a mucous degeneration of the epithelium of the nasal cavities occurs in early stages, but I cannot confirm this statement. He found the first cilia in a fetus of 5.7 cm. in the region of the lower concha and the middle meatus. In a fetus of 10.5 cm. (first half of the fifth month) they occur everywhere.

For further information concerning these structures and also for a possible function for them, see Killian (1895 1 ).

Up to the present the development of the primitive nasal cavities has alone been considered, and it must now be pointed out that, although the largest and most important part of the definitive nasal cavities arise from these, yet a portion of the primary mouth cavity becomes incorporated into the nasal cavities by the formation of the definitive palate and together with the primary nasal cavities forms the definitive ones.

It will be remembered that the primary nasal cavities open secondarily into the primary mouth cavity, the primary choanae being thus formed. With the more rapid growth of the facial region of the head these primary choanae increase in length and become slit-like. In this stage the nasal cavities are separated from the mouth cavity by the primary palatal processes (Dursy, 1869), which I do not always find well developed. These processes are formed by the margins of the primary choanae growing somewhat toward one another ; they lie in the region of the lower border of the medial frontal process and in that of the medial border of the maxillary process. The tongue, as soon as it has developed, lies close against the primitive choanae. Now (in the seventh to the eighth week) 11 the secondary palatal processes appear in the primitive mouth cavity on the inner side of the maxillary processes ; they begin at the anterior end of the primitive choanae and extend to the region of the pharynx; about their middle a projecting knob may be seen (Fig. 154, z), the anlage of the uvula.

10 More detailed statements regarding these glands have heen made by Delia Vedova (1907). This author found their first anlagen as solid processes on the inferior concha and in the middle meatus of a 9.2 cm. fetus; in a fetus of 10.5 cm. he saw lumina appearing in them, and in one of 15 cm. their tubuli were richly branched.

11 Delia Vedova (1907, 1908) gives for this, as well as for the general formation of the palate, earlier dates than do other authors.

The primary palatal processes appear at first as inconspicuous folds of the mucous membrane on the inner surface of the roots of the secondary palatal processes ; these are at first almost sagittal in position, their free edges looking downward and embracing the anlage of the tongue. This relation is shown in Figs. 138, 139, and 140.

In later stages the free edges of the secondary palatal processes are directed toward one another and the tongue is no longer between them. How this alteration in the relative positions of the palate and tongue has been brought about has been variously explained. His (1885, 1901) supposed that the tongue actively withdrew itself, 12 and if this did not happen properly a cleft palate results. In support of his view he refers to cases in which the tongue is withdrawn on one side and not on the other. Fick (1902) at first agreed with His; later he speaks in opposition to the idea of an upward bending of the palatal plates. According to his view, there must occur an extensive alteration in shape of the palatal and alveolar processes, which requires time for its accomplishment. He calls attention to a ridge in the pig, which, by further growth, produces a palatal plate having from the first its proper position above the tongue. According to this view the essential thing would be a change of form by growth and not active movement of the tongue. This is apparently the view held by Anna Polzl (1904), although her account of the process is not altogether clear to me. The closure of the secondary palate is made possible "by the tongue growing forward out of the space between the palatal plates without coming into it behind." The palatal plates themselves grow above the tongue in a horizontal direction, changing their form. Schorr (1908), who at my suggestion has recently investigated the question, comes to the conclusion that the change of position of the palatal processes is the result of a series of complicated phenomena depending on the principle of unequal growth ; the tongue and the palatal plates play quite independent parts in the process, but their parts must also be closely coordinated in order that a normal result may be brought about. The tongue changes its position and the secondary palatal processes become bent up by unequal, regular growth. A ridge, such as Fick described for the pig, Schorr could not find. "The depression and elongation of the tongue and the tendency of the palatal plates to gradually bend upwards produce a slow gliding movement between the lateral surfaces of the tongue and the medial surfaces of the palatal plates, a constant adaptation of one to the other and, in addition, a gradual change of position of one part after the other from before backwards." When the palatal plates have become bent up, they bound the secondary palatine cleft (Dursy), which becomes obliterated by the fusion of the plates. Contact between them takes place first behind their anterior ends and from there the fusion proceeds in both directions: it is completed in the eleventh or twelfth week. The epithelium originally present along the line of contact is forced out by the mesoderm, but portions of it may persist as epithelial pearls (Leboucq, 1881) and mav also give rise to cvsts (Dursy, 1869).

"His says, "This withdrawal (of the tongue) may be induced by active muscle centractions, — i.e., by depression of the lower jaw and by movements of the tongue."

Posteriorly the fusion extends as far as the uvula, which is formed from a paired anlage, — that is to say. it extends beyond the territory of the nasal cavities, and anteriorly also the plates do not fuse completely; in this region there later projects between them the anterior part of the septum, and only the nasopalatine ducts (ductus incisivi, Stenonis) persist, at first as solid cords of epithelium. After the palatal processes have fused in the median line, the two sides of the nasal cavity are still for a time continuous beneath the anlage of the septum (Fig. 142) ; later, by the fusion of the lower border of the septum with the palate, they become completely separated from each other and open by the secondary choanse into the pharynx posteriorly.

By the processes that have just been described a portion of the primary mouth cavity becomes added to the nasal cavity. In embryos one may indicate, with Schwalbe (1882, 1887, p. 51 et seq.), the boundary between the territories belonging to the primary and secondary nasal cavities by a line extending from the nasal opening of the incisive canal to the anterior inferior angle of the body of the sphenoid bone; later this line will not represent the boundary, since the posterior portions of the second and third concha 1 project beyond the line into the region of the short nasopharyngeal passage. The nasopalatine ducts, whose formation has already been described, later acquire for a time a lumen; then it disappears except at its upper and lower ends, which may to a greater or less extent persist. In the nasal cavities these remains of the nasopalatine ducts lie close to either side of the septum; on the palate they are on either side of the papilla palatina, which is formed in the region of the part of the nasal septum which takes part in the formation of the palate.

To recapitulate once more, the entire nasal floor is formed in the region jusl behind the external nares by a part of the lateral nasal process, by the premaxillary palate, by a small part of the lower border of the nasal septum, and by the anterior pari of the palatal processes of the maxilla'.

The external nares, as Kolliker (1879, p. 767) found and Retzius (1904 > and 1904 2 ), Peter (1901 2 , p. 72), and Delia Vedo (1907) have recently thoroughly demonstrated, are for a time (from the second to the sixth month, Kallius) closed by epithelial growths, formed (according to Peter), in man at least, al first only from the median walls. These epithelial masses are eg cially prominent at the anterior end of the nasal vestibule and for a time project from the external aares. Posteriorly they extend to the nasoturbinal. "In the fifth to the sixth month," according to Delia Vedova (1907) even in the fourth month, "the solution of the closure begins, apparently by the degeneration of the middle masses of epithelium. But for a long time one still finds remains of the epithelium in the open nares" (Kallius, 1905, p. 220).

The development of the nasal skeleton has been considered in connection with the skull ; only a few remarks, taken essentially from Kallius (1905, p. 212 et seq.), are necessary here. I may first point out that in the conchae of the nose the skeleton, as was formerly supposed, is not the primary structure. The swellings of the mucous membrane are the primary structures and the cartilage does not grow into these, but arises in them.

Quite briefly also the question as to the mechanism of the growth of the conchce may be considered. Schonemann (1901) confirms the view of Born and Legal (Peter, 1901 2 , p. 55) that the conchae are cut out of the lateral walls of the nasal cavities by grooves and that they are accordingly persistent portions of the nasal walls and not evaginations into the lumen of the nasal cavities; the epithelium must, therefore, grow towards those regions of the connective-tissue matrix where it finds the least resistance. Peter believes that Schonemann in this view has attributed to the connective tissue "an altogether too important part in the outgrowth of the epithelial grooves." It seems to me, on the contrary, that he underestimates the role of the connective tissue, whose growth also has its part to play in the formation and form of the concha; and elevations, and Kallius (1905, p. 203) does likewise.

The formation of the cartilage tissue begins in the seventh to the eighth week in the region of the body of the sphenoid bone. It advances thence apically in the septum; it is always further developed in this than in the lateral walls, where LI form- in the various conchae; in the wall of the inferior meatus and in the floor of the nasal cavity no cartilage forms. "When the cartili has formed in the regions mentioned, the cartilaginous skeleton (of the nose) consists of a sagittal unpaired plate in the nasal septum and of lateral paired plates, continuous with the former and forming the lateral walls and roof of the aasal cavity. Yet the union of the lateral and median plates is complete only in the anterior parts, in what will later be the roof of the external nose; posteriorly there is at first a wide opening, elongated in the sagittal direction, through which the fibres of the olfactory nerve pass. Then individual rods of cartilage develop, which divide the large opening into several smaller ones. By the increase of the partitions of the opening the cartilaginous cribriform plate is eventually formed." In a fetus of nine weeks the cartilaginous septum is continuous anteriorly with the lateral plates. These are curved in their lower portion and project into the maxilloturbinals ; they are not yet in connection with the orbital plates ; on their medial surfaces, those turned towards the septum, the anlage of the middle concha may be recognized as a quite small projection. Figs. 155 and 156 - e.g. are of a reconstruction from a fetus of twelve weeks; the small, somewhat indistinct ridge in front of the anlage of the cartilage of the middle concha (m.M.) forms the cartilaginous basis of the nasoturbinal. The orbital plates have now united with the nasal capsule; the cartilaginous anlage of the cribriform plate has not yet formed, but in its place there is a single large foramen. The Jacobson cartilages, whose development has already been described (p. 196, 197), are formed. Mention may also be made of the processus cartilagineus paranasalis (Mihalcowics), which later becomes incorporated in the upper jaw.

The cartilaginous nasal skeleton in part becomes transformed into bone (ethmoid and inferior concha) ; another portion becomes overlaid by connective-tissue osseous anlagen, and where this happens the cartilage is for the most part absorbed. The cartilaginous portion of the septum and the cartilages of the external nose of the adult are persistent portions of it. These parts do not, however, remain unchanged, but are divided by ingrowing connective tissue (Mihalcowics, 1898, 1899, 1900, Kallius, 1905). Thus the cartilaginous septum usually becomes separated from the anterior portions of the lateral cartilages and remains permanently connected with them only posteriorly; thus also are formed the alar cartilages, whose peculiar configuration begins to appear in the sixth month of uterine life.

The main points of the development of the external nose have already been described on p. 192. It was also pointed out there how greatly the parts originally lying between the nasal cavities were compressed from both sides ; this process also makes relative progress later. The entire space between the two processus globulares is represented in the fully formed individual only by the philtrum of the upper lip, the space between the entrances into the nasal cavities of the embryo only by the border of the nasal septum between the adult external nares; in this region there occurs occasionally an absolute reduction of the distance. His 13 found it in a five weeks' embryo to be 1.7 mm., in a seven weeks' one 1.2 mm., and in a somewhat older one 0.8 mm. The further formation of the external nose is dominated in later stages of development principally by the outgrowth of the middle portion of the nasal angle together with the tip of the nose, whereby the dorsum is formed. The nares, which originally looked directly forward, become directed downward ; their upper borders in the embryo lie at first very high, later, as may be perceived by a comparison with the position of the eyes, decidedly lower. The development of the individual form of the external nose begins only long after birth and lasts until puberty; it will not be followed further, but in a general way it may be remarked that the nose in women frequently retains more or less of its infantile habitus.

Fig. 156. — Reconstruction of the cartilaginous skeleton of the'right lateral wall of the nose of a human embryo of about 12 weeks. The cut surface formed by cutting through the roof of the nose is unshaded. (After Kallius, from Bardeleben's Handbuch, vol. 5, Part 1, p. 213, Fig. 78.) X 30. o. M., m. M., u. M., cartilages of the superior, middle, and inferior conch® ; K., wing of sphenoid bone; v. R., anterior border.

The development of the nasal cavities after birth has been thoroughly studied by Merkel (1885-1890) and Disse (1889). I give what are essentially the results of these investigators in the summary by Kallius (1905). "If one compares the nasal cavities of the child with those of the adult, one finds that the ethmoidal and maxillary portions are of equal height in the adult, while in the child the ethmoidal part is twice as high ; the maxillary portion must therefore gain considerably in height during growth. In the seventh year of life the definitive proportions are first acquired, and growth proceeds very slowly." In the new-born child the inferior concha reaches the floor of the nasal cavities, and the inferior meatus is therefore very narrow and the nasal exit also. The middle meatus is mainly used as the air-passage. Only after the milk dentition has fully erupted is there a better development of the nasal spaces. Thus the inferior meatus becomes pervious at about this time, although it remains quite narrow until about the seventh year. With the eruption of the molar teeth the maxilla, and with it the nasal cavities, elongates from before backward.

Cited from Kallius, 1905, p. 218.

With the formation of the body of the maxilla, which occurs at this time, its wall and the middle concha, which is fastened to this, undergo a downward movement. In this, however, the entrance into the maxillary sinus, which is of the proper size when the teeth break through, does not participate, and it therefore comes to lie at the upper part of the cavity which is enlarging downwardly.

When the change of dentition begins there is a cessation of the growth of the maxilla until puberty, when the change of the dentition is complete.

This corresponds in general with the growth of the skull, in which Merkel (1882 and 1885-1890) recognizes two periods; one lasts until the seventh year, then follows a pause, and the second period begins with puberty.

The growth relations of the upper jaw may also be determined from the position of the pharyngeal opening of the tuba auditiva; in the fetus it lies below the level of the palate, in the new-born child at its level, and in the second year of life at the level of the posterior end of the inferior concha (maxilloturbinal). Furthermore, the upper jaw is also pushed somewhat anteriorly during its growth, whereby the orthognathous face of the newborn child assumes a more or less pronounced prognathous form.

Some of the malformations in the nasal region may be explained as inhibitions of the development. The median lip cleft has already been referred to (p. 194) as an inhibition phenomenon occurring in the region of the upper lip and nasal septum. When disturbances of the formation of the primitive palate occur, the condition known as harelip is produced. To explain its formation it is not necessary to assume that the contact of the maxillary process with the processus globularis of the medial nasal process is entirely suppressed ; it may follow this, for if the growth of the mesoderm fails (see p. 193) the fused epithelia may again become separated by further growth. Naturally all variations may occur ; the lateral nasal process may come into contact with the medial one but the contact of the maxillary processes may fail, or, on the other hand, the fusion may fail in general (compare Fig. 157).

If the secondary palatal processes fail to come into contact, so that the formation of the secondary palate is incomplete, a cleft palate, palatum fissum, results. In such cases one side of the nasal cavity may be closed below by the fusion of the downgrowing septum with one of the palatal plates. A fusion of the nasal septum with the united palatal plates may also fail to occur. This inhibition is practically important if at the same time harelip occurs on both sides; then the portion of the upper lip that lies between the two clefts and the nasal septum protrude greatly, on account of the septum not being anchored posteriorly. Naturally both harelip and cleft palate may occur simultaneously.

Fig. 157. — Defective formation of the lips and palate in a fetus of about three months. X 5. (After His, Anatomie menschlicher Embryonen, Part III, p. 43, Fig. 28.)

That the septal folds may not only persist but even become hypertrophied has already been stated.

Other malformations, such as the closure of the external nares and of the choanae, receive no explanation from the developmental history and are probably to be referred to intra-uterine pathological conditions.

Pages where the terms "Historic Textbook" and "Historic Embryology" appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms and interpretations may not reflect our current scientific understanding. (More? Embryology History | Historic Embryology Papers)

Pages where the terms "Historic Textbook" and "Historic Embryology" appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms and interpretations may not reflect our current scientific understanding. (More? Embryology History | Historic Embryology Papers)